The environmental impact of burning fossil fuels is a widely recognized global issue. There are governmental and civil initiatives to diminishing this detrimental effect. Two of the major initiatives which are affecting the liquid fuel industry are the EPA regulation to limit S content of on-road fuels, and the ever increasing awareness for the need to use renewable fuels.
In order to meet emissions and fuel efficiency goals, automotive Original Equipment Manufacturers (OEM's) are investigating the use of NOx traps, particulate traps and direct injection technologies. Such traps and catalyst systems tend to be intolerant to sulfur, this coupled with the demonstrated adverse environmental consequences of burning sulfur rich fuels has resulted in a global effort to reduce the sulfur content of fuels (Reference World-Wide Fuel Charter, April 2000, Issued by ACEA, Alliance of Automobile Manufacturers, the entire teaching of which is incorporated herein by reference). These low sulfur and ultra-low sulfur fuels are becoming increasingly necessary to ensure compliance with emissions requirements over the full useful life of the latest technological generation of vehicles. Governments are also introducing further legislation for the reduction in particulate matter and fuel emissions.
In the United States, the Environmental Protection Agency (EPA) regulations require that the sulfur content of on road fuel meet the Ultra Low Sulfur specification, specifically less than 15 ppm by mass of sulfur in the finished fuel. Similar regulations are also in place globally.
The method most commonly utilized to reduce the sulfur content of fuels is referred to as “hydro-treating”. Hydro-treating is a process by which hydrogen, under pressure, in the presence of a catalyst, reacts with sulfur compounds in the fuel to form hydrogen sulfide gas and a hydrocarbon.
Globally there is a significant desire to utilize “green” or “renewable fuels” as a source of energy. These fuels are gaining popularity due to various social and political factors. The effect of petroleum fuels on carbon dioxide emissions/global warming and the dependence on foreign sources of fuel are a few of the prominent factors driving popular support.
Renewable fuels are gaining greater market acceptance as a cutter stock to extend petroleum diesel market capacity. The blends of renewable fuels with petroleum diesel are being used as a fuel for diesel engines, utilized for heating, power generation, and for locomotion with ships, boats, as well as motor vehicles.
The renewable cutter stock portion of a blended fuel is commonly known as bio-diesel. Bio-diesel is defined as fatty acid alkyl esters of vegetable or animal oils. Common oils used in bio-diesel production are rapeseed, soya, palm, palm kernel, tallow, sunflower, and used cooking oil or animal fats, although more exotic oil sources such as algae derived oils or Jetropha oil are also gaining market interest.
Bio-diesel is prepared by reacting (trans-esterification) whole oils with alcohols (mainly methanol) in the presence of a catalyst (acid or base), such as sodium hydroxide or sodium methoxide. This method of preparing bio-diesel, known as the CD process, is described in numerous patent applications (see, DE-A 4 209 779, U.S. Pat. No. 5,354,878, EP-A-56 25 04, the entire teachings of which are incorporated herein by reference).
Bio-diesel is a legally registered fuel and fuel additive with the U.S. Environmental Protection Agency (EPA). In order for a material to qualify as a bio-diesel, the fuel must meet ASTM D6751 (the entire teaching of which is incorporated herein by reference) for the United States, and EN14214 (the entire teaching of which is incorporated herein by reference) in Europe independent of the oil or fat used or the specific process employed to produce the additive. The ASTM D6751 specification is intended to insure the quality of bio-diesel to be used as a blend stock for 20% and lower blend levels, where as EN14214 is used to ensure quality in 100% bio diesel to be used independently as a fuel as well as Bio diesel to be used to prepare blends with petroleum fuels.
Renewable fuels are also being produced by newer and different processes than the traditional trans-esterification process used to produce conventional biodiesel. Examples of these modern processes include BTL (biomass to liquid) based on Fischer-Tropsch GTL (gas to liquid) technology, and “next generation” bio diesel which utilizes hydro treating of bio derived fats and oils to produce hydrocarbon fuels. Although these renewable fuels have many positive political and environmental attributes, they also have certain negative characteristics which must be taken into consideration when utilizing the material as an alternative fuel or as a blend stock for petroleum diesel. One of the properties which are of particular concern in the industry is the susceptibility of renewable fuels and renewable fuel/petroleum fuel blends to form insoluble particulates during storage.
The present invention addresses fuel industry operability concerns related to particulate formation in renewable fuels as well as renewable fuels/petroleum diesel blends.